1. Field of the Invention
The present invention relates to a method of estimating a motor torque constant, and more particularly, to a method of estimating the motor torque constant using an input current of the motor and an output speed of the motor.
2. Description of the Related Art
In general, motors have been used in various types of electric power system such as a disk drive or an optical pickup drive. Typically, the motor is driven by using a motor torque constant which indicates the relationship between an output torque and an input current of the motor. Accordingly, the well-estimated motor torque constant properly represents characteristics of the motor. The motor torque constant may be used for estimating characteristics of the motor. The motor torque constant actually changes depending on an input or an output of the motor when the motor is accelerated. However, the motor torque constant is regarded as a constant value or is calculated to be proportional to a change of a position of the motor. Thus, the motor torque constant can not represent characteristics of the motor.
U.S. Pat. No. 5,675,230 for a Method and Apparatus for Dynamic Low Voltage Spindle Motor Operation issued to John discloses a high torque constant line-to-line phase configuration during spindle motor power up and a lower effective torque constant configuration once normal run speed operation, and shows that the spindle motor torque constant Ktx is represented by ounce-inch/ampere and explained with a function of rotor position. This reference does not consider the variation of a motor torque constant during accelerating the motor.
U.S. Pat. No. 5,598,081 for a Vector Control Method for Controlling Rotor Speed of an Induction Motor issued to Okamura et al discloses a primary current being fed to a induction motor. After an excitation current and a detected torque current are obtained from the primary current, a torque value representing the detected torque current is multiplied by a predetermined motor constant to calculate a deviation between the delay torque current and the detected torque current. The torque constant is expressed by correlated inductance/flux parameter. This reference fails to calculate the variation of the motor torque constant during accelerating the motor.
U.S. Pat. No. 5,447,414 for a Constant Air Flow Control Apparatus and Method issued to Nordby et al. discloses a torque constant relating to air flow, air pressure, torque characteristics and speed characteristics, but the reference fails to show the variation of the motor torque constant.
A conventional method of estimating motor torque constant assumes that when the motor is accelerated, the motor torque constant is proportional to a position change as the output of the motor, regardless of the input current of the motor.
I have noticed that the art, as indicated by the foregoing exemplars, fails to consider that the motor torque constant actually depends on the input current during acceleration of the motor. Thus, an accurate motor torque constant can not be obtained by the conventional method. Moreover, I have found that an optimum value of the proportional constant K.sub.0 of the conventional method must be determined through trial and error, which consumes too much time for tuning a motor during development of the motor.